Belt for continuously variable transmission

ABSTRACT

A belt for a continuously variable transmission includes a metal element  32  having a rocking edge  40  between a main surface  38  and a slope  41  on the front side of the metal element in the advancing direction and a ring slot  35,  into which a metal ring assembly  31  is fitted, between an element body  34  and an ear portion  36.  The position of the center of gravity G of the metal element  32  is regulated to the outside of the rocking edge  40  and to the inside of a radially outer end  35   1  of the ring slot  35.  Therefore, a relation Vr&lt;Vg&lt;Vs is established when a speed of the rocking edge  40  at an instant when the metal element  32  leaves a driven pulley is represented by Vr, a speed of the center of gravity G of the metal element  32  is by Vg, and a speed of the ring slot  35  at the radially outer end  35   1  is by Vs, whereby the proper range of the center of gravity G of the metal element  32  of the belt for the continuously variable transmission can be specified correctly so that the metal element  32  located at a chord portion between the driven pulley  11  and a drive pulley  6  of a metal belt  15  is prevented from being tilted and thus can be meshed smoothly with the drive pulley  6.

FIELD OF THE INVENTION

The present invention relates to a belt for a continuously variabletransmission, including a large number of metal elements supported onmetal ring assemblies each of which is comprised of a plurality ofendless metal rings laminated one on another.

BACKGROUND ART

As shown in FIGS. 2 and 3, a pair of main surfaces 38 and 39 extendingperpendicular to a direction of movement and parallel to each other areprovided on front and rear sides of a metal element 32 in the directionof movement, and a slope 41 is formed radially inside the main surface38 on the front side in the direction of movement so as to be continuouswith the latter. A pair of adjacent ones of the metal elements 32 can bepitched relative to each other around a rocking edge 40 extendingbetween the main surface 38 and the slope 41. Therefore, as shown inFIG. 4, when the metal elements 32 are moved from a drive pulley 6 to adriven pulley 11, the main surfaces 38 and 39 of the adjacent ones ofthe metal elements 32 are placed in abutment against each other totransmit a driving force. When the metal elements 32 are in a statewound around the drive pulley 6 or the driven pulley 11, theinterference of the metal elements 32 with each other can be avoided bythe pitching around the rocking edge 40.

The metal elements 32 of the belt for the continuously variabletransmission perform a rectilinear translating movement in a chordportion of the belt between the drive pulley 6 and the driven pulley 11and hence, the moving speeds of various portions of the metal element 32are the same as one another. However, in a state in which the metalelements 32 are wound around the drive pulley 6 and the driven pulley11, the metal elements 32 perform a rotating movement about rotationalaxes of the drive pulley 6 and the driven pulley 11 and hence, themoving speed of a radially outer portion of the metal element 32 islarger than that of a radially inner portion of the metal element 32.

At this time, the metal elements 32 wound around the pulleys 6 and 11are brought into abutment against each other at the rocking edge 40.Therefore, the speed of the rocking edge 40 of each of the metalelements 32 wound around the pulleys 6 and 11 (the pitch circular speed)is equal to the speed of the various portions of the metal elements 32performing the rectilinear translating movement in the chord portion.Namely, the speed of the rocking edge 40 of the metal elements 32 atbelt portions wound around the pulleys 6 and 11 and the speed of therocking edge 40 of the metal elements 32 at belt portions which are notwound around the pulleys 6 and 11 (i.e., the chord portion), are thesame as each other. Therefore, in the state in which the metal elements32 are wound around the pulleys 6 and 11, the speed of the radiallyouter portion of the metal element 32 than the rocking edge 40 is largerthan the speed of the rocking edge 40, and the speed of the radiallyinner portion of the metal element 32 than the rocking edge 40 issmaller than the speed of the rocking edge 40.

Now, when the metal elements 32 lie in the chord portion between thedrive pulley 6 and the driven pulley 11 to transmit the driving force,the main surfaces 38 and 39 of adjacent ones of the metal elements 32are brought into close contact with each other and thus are preventedfrom being inclined. However, when the metal elements 32 lie in thechord portion between the driven pulley 11 and the drive pulley 6 totransmit no driving force, a small gap is produced between the adjacentones of the metal elements 32 and hence, in a portion A in FIG. 4, themetal elements 32 may be meshed with the drive pulley 6 while remaininginclined in the direction of movement (with the pitching remainingoccurred) in some cases. If the metal elements 32 are meshed with thedrive pulley 6 while remaining inclined in the direction of movement, amovement for dissolving the pitching of the metal elements 32 andcompacting the gap between the metal elements occurs in the chordportion near an outlet of the drive pulley 6 for resisting against anurging force acting between the elements and hence, the followingproblems arise: the wearing of the metal elements 32 and the pulley 6 isincreased, and the power transmitting efficiency is reduced.

Therefore, a belt for a continuously variable transmission described inJapanese Patent Application Laid-open No.2-225840 is designed so thatthe center of gravity G of the metal element 32 is located in thevicinity of the rocking edge 40 or radially outside the rocking edge 40,thereby preventing a gap from being produced between the metal elements32 in the chord portion between the driven pulley 11 and the drivepulley 6, so that the metal elements 32 in close contact with oneanother are smoothly meshed with the drive pulley 6.

More specifically, the speed of the center of gravity G of the metalelements 32 in the chord portion between the pulleys 6 and 11 is equalto the pitch circular speed, but the speed of the center of gravity G ofthe metal elements 32 wound around the pulleys 6 and 11 is larger thanthe pitch circular speed, if the center of gravity G lies radiallyoutside the rocking edge 40. In other words, the kinetic energy of themetal elements 32 leaving the driven pulley 11 is larger than thekinetic energy of the metal elements 32 lying in the chord portion. Themetal elements 32 lying in the chord portion are urged forwards (towardthe drive pulley 6) by a difference between the kinetic energies and aresmoothly meshed with the drive pulley 6 in a state placed in closecontact with one another.

In the prior art described above, the center of gravity G of the metalelement 32 is allowed to lie radially inside the rocking edge 40 even ata distance of 0.5 mm from the latter. However, if the center of gravityG lies radially inside the rocking edge 40, the kinetic energy of themetal element 32 leaving the driven pulley 11 becomes smaller than thatof a metal element 32 lying in the chord portion and hence, the metalelements 32 lying in the chord portion cannot be meshed with the drivepulley 6 without being pitched in a state placed in close contact withone another. Therefore, it is required that the center of gravity G ofthe metal element 32 should lie radially outside the rocking edge 40. Inother words, it is required that a relation Vr<Vg should be establishedwhen Vr represents a speed of the rocking edge 40 at an instant when themetal element 32 leaves the driven pulley 11, and Vg represents a speedof the center of gravity G of the metal element 32.

Additionally, if the center of gravity G of the metal element 32 movesradially outside too away from the rocking edge 40, the kinetic energyof the metal elements 32 which have left the driven pulley 11 becomesexcessive and the metal elements 32 rotate so as to fall forwards, asshown in FIG. 10. As a result, the energy is expended by theinterference between a metal ring assembly 31 and a lower portion of anear portion 36, or by the interference of coupling, thereby resulting inloss of a force for delivering the metal elements 32 forwards.Therefore, there is a possibility that the metal elements 32 could notbe meshed with the drive pulley 6 in the state free of the pitching.

DISCLOSURE OF THE INVENTION

The present invention has been accomplished with the above circumstancesin view, and it is an object of the present invention to ensure that thecenter of gravity of the metal elements is defined correctly in a properrange, whereby the metal elements lying in the chord portion are meshedwith the drive pulley in the state free of the pitching.

To achieve the above object, according to the present invention, thereis provided a belt for a continuously variable transmission, comprisinga large number of metal elements supported on metal ring assemblies eachof which is comprised of a plurality of endless metal rings laminatedone on another, the belt being wound around a drive pulley and a drivenpulley to transmit a driving force between both of the pulleys,characterized in that the metal elements include ring slots forsupporting the metal ring assemblies, and are pitchably in abutmentagainst one another with a rocking edge interposed therebetween, and thefollowing relation is established:

Vr<Vg<Vs

wherein Vr represents a speed of the rocking edge at an instant when themetal element leaves the driven pulley; Vg represents a speed of thecenter of gravity of the metal element; and Vs represents a speed of aradially outer end of the ring slot.

With the above arrangement, the speed Vg of the center of gravity of themetal elements is set larger than the speed Vr of the rocking edge at aninstant when the metal elements leave the driven pulley. Therefore, themetal elements leaving the driven pulley have a kinetic energy largerthan the metal elements lying in the chord portion, whereby the metalelements lying in the chord portion can forcibly be urged forwards andmeshed with the drive pulley in a state placed in close contact with oneanother without being pitched. In addition, the speed Vg of the centerof gravity of the metal elements is set smaller than the speed Vs of theradially outer end of the ring slot. Therefore, it can be avoidedpreviously that the metal elements leaving the driven pulley are fallendown in a direction of movement with an excessive kinetic energy,whereby the metal elements lying in the chord portion can be smoothlybrought into close contact with one another and meshed with the drivepulley without being pitched.

In addition to the above arrangement, there is provided a belt for acontinuously variable transmission, wherein a relation, Vr<Vk<Vg<Vs isestablished when Vk represents the speed of a radially inner end of thering slot of the metal element.

With the above arrangement, when an action for compacting a gap betweenthe metal elements occurs at the chord portion extending from the drivenpulley toward the drive pulley, a pitching moment acting on the metalelements can be reduced to enable the metal elements to be smoothlybrought into close contact with one another.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 9 show an embodiment of the present invention.

FIG. 1 is a skeleton illustration of a power transmitting system in avehicle having a continuously variable transmission mounted thereon;

FIG. 2 is a perspective view of a metal belt section;

FIG. 3 is a view taken in the direction of an arrow 3 in FIG. 2;

FIG. 4 is a view of a metal belt wound around a drive pulley and adriven pulley;

FIG. 5 is a view for explaining a technique for regulating the center ofgravity of a metal element;

FIG. 6 is a view for explaining a relation, Vr<Vk<Vg<Vs, correspondingto FIG. 3;

FIG. 7 is a view showing a dimension of each portion of the metalelement;

FIG. 8 is a view showing each region of the metal belt;

FIG. 9 is a graph showing a variation of speeding each region of themetal belt; and

FIG. 10 is a view for explaining the problems of the prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

The mode for carrying out the present invention will now be described byway of an embodiment of the present invention shown in the accompanyingdrawings.

FIG. 1 shows the skeleton structure of a metal belt-type continuouslyvariable transmission T mounted on an automobile. An input shaft 3 isconnected to a crankshaft 1 of an engine E through a damper 2 and alsoconnected to a drive shaft 5 of the metal belt-type continuouslyvariable transmission T through a starting clutch 4. A drive pulley 6 ismounted on the drive shaft 5 and includes a stationary pulley half 7secured to the drive shaft 5, and a movable pulley half 8 which ismovable toward and away from the stationary pulley half 7. The movablepulley half 8 is biased toward the stationary pulley half 7 by ahydraulic pressure applied to an oil chamber 9.

A driven pulley 11 is mounted on a driven shaft 10 disposed in parallelto the drive shaft 5, and includes a stationary pulley half 12 securedto the driven shaft 10, and a movable pulley half 13 which is movabletoward and away from the stationary pulley half 12. The movable pulleyhalf 13 is biased toward the stationary pulley half 12 by a hydraulicpressure applied to an oil chamber 14. A metal belt 15 comprising alarge number of metal elements 32 supported on a pair of left and rightmetal ring assemblies 31, 31 is wound between the drive pulley 6 and thedriven pulley 11 (see FIG. 2) . Each of the metal ring assemblies 31comprises twelve metal rings 33 laminated one on another.

A forward drive gear 16 and a backward drive gear 17 are rotatablycarried on the driven shaft 10 and are capable of being selectivelycoupled to the driven shaft 10 by a selector 18. Secured to an outputshaft 19 disposed in parallel to the driven shaft 10 are a forwarddriven gear 20 meshed with the forward drive gear 16, and a backwarddriven gear 22 meshed with the backward drive gear 17 through a backwardidle gear 21.

The rotation of the output shaft 19 is inputted to a differential 25through a final drive gear 23 and a final driven gear 24 and thentransmitted from the differential 25 through left and right axles 26, 26to driven wheels W, W.

A driving force from the engine E is transmitted through the crankshaft1, the damper 2, the input shaft 3, the starting clutch 4, the driveshaft 5, the drive pulley 6, the metal belt 15 and the driven pulley 11to the driven shaft 10. When a forward travel range is selected, thedriving force of the driven shaft 10 is transmitted through the forwarddrive gear 16 and the forward driven gear 20 to the output shaft 19 tomove the vehicle forwards. When a backward travel range is selected, thedriving force of the driven shaft 10 is transmitted through the backwarddrive gear 17, the backward idle gear 21 and the backward driven gear 22to the output shaft 19 to move the vehicle backwards.

During this time, the shift ratio is continuously regulated bycontrolling the hydraulic pressures applied to the oil chamber 9 in thedrive pulley 6 and the oil chamber 14 in the driven pulley 11 of themetal belt-type continuously variable transmission T by a hydraulicpressure control unit U₂ which is operated by a command from anelectronic control unit U₁. More specifically, if the hydraulic pressureapplied to the oil chamber 14 in the driven pulley 11 is increasedrelative to the hydraulic pressure applied to the oil chamber 9 in thedrive pulley 6, a groove width of the driven pulley 11 is decreased,leading to an increased effective radius. Attendant on this, a groovewidth of the drive pulley 6 is increased, leading to a decreasedeffective radius. Therefore, the shift ratio of the metal belt-typecontinuously variable transmission T is varied continuously toward“LOW”. Reversely, if the hydraulic pressure applied to the oil chamber 9in the drive pulley 6 is increased relative to the hydraulic pressureapplied to the oil chamber 14 in the driven pulley 11, the groove widthof the drive pulley 6 is decreased, leading to an increased effectiveradius. Attendant on this, the groove width of the driven pulley 11 isincreased, leading to a decreased effective radius. Therefore, the shiftratio of the metal belt-type continuously variable transmission T isvaried continuously toward “OD”.

As shown in FIGS. 2 and 3, the metal element 32 formed from 10 a metalplate by punching includes a substantially trapezoidal element body 34,and a substantially triangular ear portion 36 connected to an upperportion of the element body 34 through a pair of left and right ringslots 35, 35 into which the metal ring assemblies 31, 31 are fitted. Apair of pulley abutment surfaces 37, 37 are formed on left and rightopposite edges of the element body 34, and are capable of abuttingagainst V-surfaces of the drive pulley 6 and the driven pulley 11. Apair of front and rear main surfaces 38 and 39 perpendicular to adirection of movement and parallel to each other are formed on front andrear sides of the metal element 32 in the direction of movement, and aslope 41 is formed below the main surface 38 on the front side in thedirection of movement with a laterally extending rocking edge 40interposed therebetween. Further, a projection 42 and a recess 43 areformed respectively on the main surface 38 on the front side in thedirection of movement and the main surface 39 on the rear side in thedirection of movement, which correspond to the ear portion 36.

As can be seen from FIG. 3, a center of gravity G of the metal element32 is located radially outside the rocking edge 40 and radially insidethe radially outer ends 35 ₁, 35 ₁ of the ring slots 35, 35. In otherwords, when the speed of the rocking edge 40 at an instant when themetal element 32 leaves the driven pulley 11 is represented by Vr; thespeed of the center of gravity G of the metal element 32 is by Vg; andthe speed of the radially outer ends 35 ₁, 35 ₁ of the ring slots 35, 35is by Vs, a relation, Vr<Vg<Vs is established.

As shown in FIG. 4, the adjacent ones of the metal elements 32 lying inan advancing-side chord portion extending from the drive pulley 6 towardthe driven pulley 11 (i.e., a chord portion capable of transmitting thedriving force) transmit the driving force in a state in which the mainsurfaces 38 of the front side of the metal element 32 and the mainsurface 39 of the rear side of the metal element 32 are in abutmentagainst each other, and the projection 42 of the front side of the metalelement 32 has been fitted in the recess 43 of the rear side of themetal element 32. The metal elements 32 wound around the drive pulley 6and the driven pulley 11 are swung around the rocking edge 40 byreleasing of the contact of the main surfaces 38 and 39 with each other,and are arranged radiately in a radial direction of the pulleys 6 and11.

On the other hand, a small gap is produced at an outlet side of thedriven pulley 11 between the metal elements 32 lying in a returning-sidechord portion extending from the driven pulley 11 toward the drivepulley 6 (i.e., a chord portion incapable of transmitting the drivingforce). For this reason, the metal elements 32, which cannot maintainthe attitude with the main surfaces 38 and 39 put into abutment againsteach other, are liable to be inclined. In this embodiment, however,since the speed Vg of the center of gravity G of the metal element 32 isset larger than the speed Vr of the rocking edge 40 at an instant whenthe metal element 32 is moved away from the driven pulley 11, the metalelement 32 leaving the driven pulley 11 is released to thereturning-side chord portion with a kinetic energy larger than that ofthe metal element 32 lying in the returning-side chord portion.Therefore, the element 32 on the chord portion can be forcibly urgedtoward the drive pulley 6 with such vigor. As a result, the gap producedat the outlet side of the driven pulley 11 between the metal elements 32on the returning-side chord portion is gradually decreased asapproaching the drive pulley 6 and moreover, the inclined metal elements32 are gradually risen and arranged in close contact with one another atthe inlet side of the drive pulley 6, whereby they are meshed with thedrive pulley 6 in an attitude free of pitching. Thus, it is possible toeliminate a problem that the wearing of the metal elements 32 and thedrive pulley 6 is increased, and a problem that the power transmittingefficiency is reduced.

Moreover, since the speed Vg of the center of gravity G of the metalelement 32 is set smaller than the speed Vs of the radially outer ends35 ₁, 35 ₁ of the ring slots 35, 35, it can be prevented that the metalelement 32 leaving the driven pulley 11 has an excessive kinetic energyto generate a large moment around the metal ring assemblies 31, 31, andthe falling of the metal element 32 in the pitching direction can bepreviously avoided, whereby the metal elements 32 can be brought intoclose contact with one another and smoothly meshed with the drive pulley6.

FIG. 5 shows a technique for regulating the position of the center ofgravity G of the metal element 32. To move the center of gravity G ofthe metal element 32 radially outwards (upwards in FIG. 5), the loweredge of the element body 34 may be changed to a position 34 ₁, and/orthe upper edge of the ear portion 36 may be changed to a position 36 ₁.To move the center of gravity G of the metal element 32 radially inwards(downwards in FIG. 5), the lower edge of the element body 34 may bechanged to a position 34 ₂, and/or the upper edge of the ear portion 36may be changed to a position 36 ₂.

It should be noted here that in addition to the above-describedrelation, Vr<Vg<Vs, when the speed of radially inner ends 35 ₂, 35 ₂ ofthe ring slots 35, 35 (a saddle surface speed) is represented by Vk, ifthe relation Vr<Vk<Vg<Vs is established, further effects can beobtained, which will be described with reference to FIGS. 4 and 6 to 9.

As shown in FIG. 6, small vertical drags N, N act between the radiallyouter ends 35 ₁, 35 ₁ and the radially inner ends 35 ₂, 35 ₂ of the ringslots 35, 35 and the metal ring assemblies 31, 31 even in the chordportion on which the urging force acting between the elements does notact. An inner peripheral speed Va and an outer peripheral speed Vb ofthe metal ring assemblies 31, 31 in the chord portion are not the sameas the speed Vr of the rocking edge 40 in the metal element 32, and therelation is Va>Vr and Vb>Vr as will be described below.

In the chord portion with which the metal elements 32 move in parallel,the speed Vr of the rocking edge 40 of the metal element 32 accords withthe speed Vk of the radially inner ends 35 ₂, 35 ₂ and the speed Vs ofthe radially outer ends 35 ₁, 35 ₁ of the ring slots 35, 35. Therefore,if the inner peripheral surfaces of the metal ring assemblies 31, 31interfere with the radially inner ends 35 ₂, 35 ₂ of the ring slots 35,35, the metal element 32 having a low speed is driven forwards by themetal ring assemblies 31, 31 having a high speed due to the frictionforce. Furthermore, if the outer peripheral surfaces of the metal ringassemblies 31, 31 interfere with the radially outer ends 35 ₁, 35 ₁ ofthe ring slots 35, 35, the metal element 32 having a low speed is drivenforwards by the metal ring assemblies 31, 31 having a high speed due toa friction force. As a result, an action for compacting the gap betweenthe metal elements 32 occurs in the chord portion.

Here, the reason why the relations, Va>Vr and Vb>Vr are established willbe described below.

In FIG. 4, when the speed of the rocking edge 40 of the metal element 32in the chord portion between the drive pulley 6 and the driven pulley 11(the speed of a pitch line) is represented by Vr, an angular speed ofthe drive pulley 6 is by ω_(DR), an angular speed of the driven pulley11 by ω_(DN), a pitch radius of the drive pulley 6 by R_(DR), and apitch radius of the driven pulley 11 by R_(DN), the following equationsare established:

ω_(Dr) =Vr/R _(DR)

ω_(DN) =Vr/R _(DN)

Here, when d represents the difference between the radius of radiallyinner ends 35 ₂, 35 ₂ of the ring slots 35, 35 (a radius of the saddlesurface) and the pitch radii R_(DR), R_(DN), the speeds Vk_(DR) andVk_(DN) of the radially inner ends 35 ₂, 35 ₂ of the ring slots 35, 35in the drive pulley 6 and the driven pulley 11 (a saddle surface speed)are given by the following equations, respectively:

VK _(DR)=(R _(DR) +d)*ω_(DR)=(R _(DR) +d)*(Vr/R _(DR))

Vk _(DN)=(R _(DN) +d)*ω_(DN)=(R _(DN) +d)*(Vr/R _(DN))

When the shift ratio is in the “LOW” side from 1.0, at the side of thedriven pulley 11, the radially inner ends 35 ₂, 35 ₂ of the ring slots35, 35 and each layer of the metal ring 33 rotate substantially withoutrelative slipping. Therefore, the inner peripheral speed Va of the metalring assemblies 31, 31 is substantially the same as the speed Vk_(DN) ofthe radially inner ends 35 ₂, 35 ₂ of the ring slots 35, 35 in thedriven pulley 11.

Therefore, if the difference between the inner peripheral speed Va ofthe metal ring assemblies 31, 31 in the chord portion and the speed Vrof the rocking edge 40 is calculated, the following equation can beobtained: $\begin{matrix}{{{Va} - {Vr}} = \quad {{Vk}_{DN} - {Vr}}} \\{= \quad {{\left( {R_{DN} + d} \right)*\left( {{Vr}/R_{DN}} \right)} - {Vr}}} \\{= \quad {{\left( {d/R_{DN}} \right)*{Vr}} > 0}}\end{matrix}$

and the inner peripheral speed Va of the metal ring assemblies 31, 31 islarger than the speed Vr of the rocking edge 40.

Further, when the shift ratio is in the “OD” side from 1.0, at the sideof the drive pulley 6, the radially inner ends 35 ₂, 35 ₂ of the ringslots 35, 35 and each layer of the metal ring 33 rotate substantiallywithout relative slipping. Therefore, the inner peripheral speed Va ofthe metal ring assemblies 31, 31 is substantially the same as the speedVk_(DR) of the radially inner ends 35 ₂, 35 ₂ of the ring slots 35, 35in the drive pulley 6.

Therefore, if the difference between the inner peripheral speed Va ofthe metal ring assemblies 31, 31 in the chord portion and the speed Vrof the rocking edge 40 is calculated, the following equation can beobtained: $\begin{matrix}{{{Va} - {Vr}} = \quad {{Vk}_{DR} - {Vr}}} \\{= \quad {{\left( {R_{DR} + d} \right)*\left( {{Vr}/R_{DR}} \right)} - {Vr}}} \\{= \quad {{\left( {d/R_{DR}} \right)*{Vr}} > 0}}\end{matrix}$

and the inner peripheral speed Va of the metal ring assemblies 31, 31 islarger than the speed Vr of the rocking edge 40.

From the foregoing, the relation, Va>Vr is established in all the shiftratios.

On the other hand, the difference Vb−Vr between the outer peripheralspeed Vb of the metal ring assemblies 31, 31 and the speed Vr of therocking edge 40 can be obtained by defining the thickness of the metalring assemblies 31, 31 as t and replacing d of the above theory withd+t. More specifically, when the shift ratio is in the “LOW” side from1.0, at the side of the driven pulley 11, the outer peripheral speed Vbof the metal ring assemblies 31, 31 is substantially the same as thespeed Vs_(DN) of the radially outer ends 35 ₁, 35 ₁ of the ring slots35, 35 and hence, the following equation can be obtained:$\begin{matrix}{{{Vb} - {Vr}} = \quad {{Vs}_{DN} - {Vr}}} \\{= \quad {{\left( {R_{DN} + d + t} \right)*\left( {{Vr}/R_{DN}} \right)} - {Vr}}} \\{= \quad {{\left\{ {\left( {d + t} \right)/R_{DN}} \right\}*{Vr}} > 0}}\end{matrix}$

and the outer peripheral speed Vb of the metal ring assemblies 31, 31 islarger than the speed Vr of the rocking edge 40.

When the shift ratio is in the “OD” side from 1.0, at the side of thedrive pulley 6, the outer peripheral speed Vb of the metal ringassemblies 31, 31 is substantially the same as the speed Vs_(DR) of theradially outer ends 35 ₁, 35 ₁ of the ring slots 35, 35 and hence, thefollowing equation can be obtained: $\begin{matrix}{{{Vb} - {Vr}} = \quad {{Vs}_{DR} - {Vr}}} \\{= \quad {{\left( {R_{DR} + d + t} \right)*\left( {{Vr}/R_{DR}} \right)} - {Vr}}} \\{= \quad {{\left\{ {\left( {d + t} \right)/R_{DR}} \right\}*{Vr}} > 0}}\end{matrix}$

and the outer peripheral speed Vb of the metal ring assemblies 31, 31 islarger than the speed Vr of the rocking edge 40.

From the foregoing, the relation, Vb>Vr is established in all the shiftratios.

TABLE 1 Speed of each portion in the advancing direction of the belt(m/sec) Chord Wound portion D portions Wound portion Name of portion ofDR pulley A, C B of DN pulley Vs Outer end of 43.79 41.66 45.16 slot VbOuter periphery 43.67 43.67 43.67 of ring Va Inner periphery 42.30 42.3042.30 of ring Vk Inner end of 42.30 41.66 42.69 slot Vr Rocking edge41.66 41.66 41.66 Vg Center of 42.60 41.66 43.20 gravity

Table 1 and FIG. 9 show variations in the speeds Vs, Vb, Va, Vk, Vr andVg of respective portions of the metal ring 15 at each of regions A, B,C and D when the transmission is operated 10 at the maximum output withan input torque of 14.4 kgf-m, an input rotational speed of 6000 rpm anda shift ratio of 0.61 using the metal belt 15 having the metal elements32 of the dimension shown in FIG. 7. The definition of each of theregions A, B, C and D of the metal ring 15 is shown in FIG. 8.

As is apparent from Table 1 and FIG. 9, it can be seen that in the chordportions A and C at which the metal elements 32 move in parallel, thespeed Vs of the radially outer ends 35 ₁, 35 ₁ of the ring slots 35, 35,the speed Vk of the radially inner ends 35 ₂, 35 ₂ of the ring slots 35,35, the speed Vr of the rocking edge 40 and the speed Vg of the centerof gravity G are the same, and that the outer and inner peripheralspeeds Vb and Va of the metal ring assemblies 31, 31 exceed the speedsVs, Vk, Vr and Vg of each of the portions of the metal element 32.Additionally, it can be seen that the speed Vg of the center of gravityG in the regions B and D where the metal elements 32 are wound aroundthe driven pulley 11 and the drive pulley 6 exceeds the speed Vg of thecenter of gravity G in the chord portions A and C.

Now, returning to the explanation of FIG. 6, in the chord portion onwhich the urging force acting between the elements does not act, thefrictional forces μN, μN (μ is a coefficient of friction) acting fromthe metal ring assemblies 31, 31 to the metal element 32 by the verticaldrags N, N act on the radially outer ends 35 ₁, 35 ₁ or radially innerends 35 ₂, 35 ₂ of the ring slots 35, 35. Even when points of action ofthe frictional forces μN, μN are in either of the radially outer ends 35₁, 35 ₁ or the radially inner ends 35 ₂, 35 ₂ of the ring slots 35, 35,if the center of gravity G of the metal element 32 is positioned betweenthe radially outer ends 35 ₁, 35 ₁ and the radially inner ends 35 ₂, 35₂ of the ring slots 35, 35, a moment, which is generated around thecenter of gravity G by the frictional force μN acting on the radiallyouter ends 35 ₁, 35 ₁ of the ring slots 35, 35 or the frictional forceμN acting on the radially inner ends 35 ₂, 35 ₂ can be maintained toS×μN or less where S represents the width of the ring slots 35, 35.

If the center of gravity G deviates from the range between the radiallyouter ends 35 ₁, 35 ₁ and the radially inner ends 35 ₂, 35 ₂ of the ringslots 35, 35, a relatively large moment exceeding S×μN acts around thecenter of gravity G, whereby a possibility arises that the behavior ofthe metal element 32 might be unstable in the chord portion on which theurging force acting between the elements does not act. Therefore, inorder to stabilize the behavior of the metal element 32 in the chordportion, it is required that the relation, Vk<Vg<Vs should beestablished at least at an instant when the metal element 32 leaves thedriven pulley 11, by positioning the center of gravity G of the metalelement 32 between the radially outer ends 35 ₁, 35 ₁ and the radiallyinner ends 35 ₂, 35 ₂ of the ring slots 35, 35.

Further, as is described in, it is required that the relation, Vr<Vgshould be established between the speed Vr of the rocking edge 40 andthe speed Vg of the center of gravity G at an instant when the metalelement 32 leaves the driven pulley 11, and that the relation Vr<Vkshould be established between the speed Vr of the rocking edge 40 andthe speed Vk of the radially inner ends 35 ₂, 35 ₂ of the ring slots 35,35 in a general design of the metal belt 15. Considering them, it isrequired that the relation, Vr<Vk<Vg <Vs should finally be established.If the relation, Vr<Vk<Vg <Vs is established, even when the action forcompacting the gap between the metal elements 32 occurs in the chordportion extending from the driven pulley 11 toward the drive pulley 6,it is possible to maintain the pitching moment for falling the metalelement 32 to the minimum and to smoothly bring the metal elements 32 inclose contact with each other.

Although the embodiment of the present invention has been described indetail, it will be understood that the present invention is not limitedto the above-described embodiment, and various modifications in designmay be made without departing from the subject matter of the invention.

What is claimed is:
 1. A belt for a continuously variable transmission,comprising a large number of metal elements (32) supported on metal ringassemblies (31) each of which is comprised of a plurality of endlessmetal rings (33) laminated one on another, said belt being wound arounda drive pulley (6) and a driven pulley (11) to transmit a driving forcebetween both of said pulleys (6 and 11), characterized in that saidmetal elements (32) include ring slots (35) for supporting said metalring assemblies (31), and are pitchably in abutment against one anotherwith a rocking edge (40) interposed therebetween, and the followingrelation is established: Vr<Vg<Vs wherein, at an instant when said metalelement (32) leaves said driven pulley (11), Vr represents a speed ofthe said rocking edge (40); Vg represents a speed of the center ofgravity (G) of said metal element (32); and Vs represents a speed of aradially outer end (35 ₁) of said ring slot (35).
 2. A belt for acontinuously variable transmission according to claim 1, wherein thefollowing relation is established: Vr<Vk<Vg<Vs when Vk represents thespeed of a radially inner end (35 ₂) of said ring slot (35) of saidmetal element (32).